Oxygen sensing devices for detecting oxygen concentration in a gas mixture are well known in the art. The oxygen sensor is constructed to generate an electrical signal responsive to the oxygen content of a gas. Stabilized zironium oxide has been employed as the main element of the oxygen sensor. This stabilized zironium oxide exhibits a conductivity by means of oxygen ions which transfer therethrough. As is well known, if some gas mixture whose partial oxygen pressure or absolute oxygen pressure must be measured is present on one side of an electrolyte and, simultaneously, a reference gas having a known partial oxygen pressure is present on the other side, a considerable voltage difference is generated by the driving force for movement of the oxygen ions between the gases through the electrolyte. The magnitude of the voltage difference is generally estimated by the Nernst equation: EQU E=(RT/4F)1n (P.sub.1 P.sub.2)
where:
R . . . gas constant
T . . . absolute temperature
F . . . Faraday constant
P.sub.1 . . . partial oxygen pressure of the reference gas
P.sub.2 . . . partial oxygen pressure of the unkown gas
Systems for determining the oxygen activity in molten metals, particularly in the production of steel, also are known in the art.
Gas probes are intended for long time usage. Most probes for molten metals, however, are intended for short term measurements, i.e., usually 30 to 60 seconds, as they cannot survive in the molten metal environment. In determining the oxygen activity of molten steel, for example, the probe is usually inserted just before pouring.